1. Field of the Invention
The present invention relates to methods and systems for controlling and adjusting traffic light timing patterns, and more particularly, to a method and system for controlling and adjusting traffic light timing patterns based on input variables related to known or predicted events, and for gradually changing traffic light intervals over time.
2. Description of the Related Art
Traffic light sequences/phases are computer-controlled and are generally timed according to a fixed schedule to accommodate common patterns of traffic flow, such as a green light for a long duration on major roads, with a correspondingly shorter duration for the intersecting minor roads. Changes to traffic light timing patterns are nearly exclusively enabled by designated time intervals, in which a discrete change is made from one timing pattern to another in response to regularly scheduled events such as weekday rush hour traffic periods.
Various methods and systems for controlling traffic light timing patterns exist. Five specific types of conventional methods and systems for controlling traffic light timing patterns include “fixed time control,” “dynamic control,” “time of day/special events,” “coordinated control,” “actuated control,” and “preemption,” each of which are discussed in further detail below. For each type, the timing cycle of the affected traffic light is changed in a discrete manner, i.e., either a regularly scheduled time interval based-change, or an abrupt change from one timing cycle to a different timing cycle.
“Fixed time control” is the simplest and most common system for controlling traffic signal timing patterns. Fixed time control is based on a fixed mechanical cycle in which the duration of each individual light (e.g., red light and green light phases of the cross street and the main street directions of an intersection) is constant. This system has no ability to improve the flow of traffic during times of heavy traffic flow over the course of a day.
A fixed time control system traffic signal timing pattern may be altered by a control system that is programmed to change the traffic signal timing pattern based on time of day or in a “special events” situation. For example, at night when there is less typically traffic, a green light phase may be set for a longer duration in the main street direction compared with the same green light phase's daily duration. Additionally, during a special event when an increase in traffic flow is anticipated, a green light phase, for example, may be set for a longer duration in the main street direction compared with the same green light phase's typical daily duration. These alterations in the fixed time control system traffic signal timing pattern represent abrupt and discrete changes effected for a specific time of day, or for a one-time or special event.
“Dynamic control” is a system designed to alter the fixed traffic signal timing patterns established by the fixed time control system. This system alters the fixed traffic signal timing patterns via, e.g., automobile sensors (electronic detector loops) embedded in the road. Automobiles waiting at an intersection in front of a red light are sensed by the sensors. These sensors send a signal to a traffic signal controller, which effects a change in the fixed traffic signal timing pattern converting the red light to green prior to the normal conversion time established by the fixed time control system. This system requires special equipment and expensive installation procedures, and does not extend the length of traffic light duration (e.g., green light phase in the heavy traffic flow direction) to accommodate known or planned increases in traffic. In short, it is noted that a “dynamic control” system requires real time sensors which provide the system with traffic volume data at the time it occurs. Before this point in time, no traffic volume information is available or known to the present system.
“Coordinated control” is a system designed to improve traffic flow by timing subsequent lights to be green (“cascading”) so that automobiles obeying the speed limit typically do not encounter any red lights for a long distance. This system is most effective in times of constant levels of traffic flow. This system is not as effective during times of anticipated increases in entering or exiting traffic volume. In fact, a system of coordinated control of traffic lights along a main road may be an obstacle to overcome in the case of a scheduled event producing irregular traffic patterns due to anticipated volume increases. Some systems can coordinate traffic lights in real time in response to increases in traffic flow. However, these systems require a large number of sensors and/or video cameras and are very expensive.
“Actuated control” is a system that includes a button that can be pressed by pedestrians at a pedestrian crossing to alter the traffic signal timing pattern. For example, this system is manually initiated by a pedestrian pressing a button to request a red light in the main street direction in order to cross a cross street safely, and to activate red lights and traffic gates at a railroad crossing.
“Preemption” systems (e.g., 3M Opticon system) are configured to allow a traffic signal timing pattern to be interrupted by certain priority traffic, such as emergency vehicles. These systems include sensors on or near the traffic signal, and are configured to receive signals from transmitters attached to the emergency vehicle that send strobe light, radio waves, audio, and/or infrared signals to the sensor. Upon initiation, the normal traffic signal timing pattern is preempted, i.e., a red light is changed to a green light in the direction of the emergency vehicle, while the cross street light is changed to red. This system is no longer used in some places, because it has been illegally replicated and used by non-emergency workers. Neither the actuated nor the preemption system applies to alterations of traffic signal durations for any more than a one-time change.
In FIG. 1, a flowchart F100 illustrating a conventional traffic light control system is shown. Data flow relating to the same is also shown. The traffic light control application system 160 is shown interconnected to a plurality of input modules. Each of the input modules are programmed and/or structured to cause the traffic light control application system module 160 to effectuate an abrupt, discrete change(s) to traffic light operations 170. The input modules include a standard traffic light timing schedule input module 130 (including static timing schedules which are in effect the majority of the time), time-based overrides input module 150 (including discrete changes which take effect over a pre-defined time interval such as rush hour), and traffic light manual override capability input module 140. The traffic light manual override capability input module 140 is interconnected to three manual override input modules, including event manual override input module 105 (e.g., manual overrides by event traffic control personnel for a “special event” as described above), emergency vehicle activation manual override input module 110, and lane sensor manual override input module 120. The input modules also include a traffic light infrastructure database input module 200, which includes a database of traffic light locations and default timing schedules as an input to the traffic light control application system 160. Data transferred from any one of these input modules to the traffic light control application system 160 results in abrupt, discrete changes in traffic light operations 170.
In FIG. 2, a flowchart F200 illustrating a conventional method for controlling a set of traffic lights based on an output of an algorithm is shown, including steps S210, S220, and S230.
UK Nos. 8730016 and 8730015 (“Cherrill et. al.”) each disclose a traffic control system which employs a model which shows, for each road intersection, the predicted vehicle arrivals over each of a number of periods, for example, 32 four-second periods. The vehicle arrival figures are used, in conjunction with traffic light pattern indications to develop vehicle queue figures, and these are utilized to optimize the traffic light patterns to minimize delay at each intersection. The model is constructed by projecting predicted patterns of vehicles leaving the intersections, to generate predicted vehicle arrivals at downstream intersections. When used in an online mode, the predicted vehicle arrival figures for the first few periods of each intersection arrival pattern are continuously replaced by predicted vehicle arrival figures obtained from vehicle sensors located upstream of the intersections. The arrival figures derived from the sensors are noted as the most accurate, and the accuracy of each predicted arrival pattern decreases as the prediction period increases. Two suggestions are made to compensate for this lowered accuracy for the long-term portions of the arrival predictions. First, the sensor counts, before replacing the corresponding predicted arrival figures, are compared with these figures to produce a flow correction factor. This correction factor represents the actual average flow of vehicles approaching an intersection over the predicted average flow of these vehicles. The predictions for each intersection are then corrected by multiplying them by the corresponding flow correction factor. Second, the queue date derived from the arrival predictions is differently weighed before it is used to optimize the light settings, these weightings diminishing from the earliest to the most future predictions.
In short, it is noted that Cherrill et. al. shows the continuous replacement of vehicle arrival predictions that forms an iterative refinement of the model, which requires the use of upstream traffic sensor equipment.
U.S. Pat. No. 6,633,238 (Lemelson et. al.) describe a system and method for controlling traffic and traffic lights, and selectively distributing warning messages to the motorists. The method described relies on a system of traffic sensing devices to determine current, real time traffic volume, and includes GPS (Global Positioning Satellite) technology to assist in communication of traffic-related messages to vehicle drivers and to dynamic traffic message display devices. Lemelson et. al. disclose as an object of the invention to select particular fuzzy logic inference rules for traffic light control based on particular conditions that may affect traffic flow such as weather or predicted unusual traffic conditions such as those that might be encountered with special events such as major sport attractions. The Lemelson et. al. system provides that outside factors may influence the decisions of the fuzzy logic expert system. Such outside factors may include inclement weather, an accident at a nearby intersection, or special event traffic patterns (i.e. sporting events, concerts, etc.).
It is noted that Lemelson et. al. describe the use of “fuzzy logic,” as referenced above, to alter the synchronization of traffic signals to adapt to detected changes in real time traffic patterns. The information tracked and collected is not known in advance to the system. As an example, suppose it is known that a major sold out rock concert is scheduled for a certain venue, date, time, and duration, after which an expected volume of traffic will be exiting the venue, following a typical statistical distribution. The system and method taught by Lemelson et. al. would not be aware of this expected disruption in normal traffic patterns until it was actually happening and detected in real-time.
Description Of the Related Art Section Disclaimer: To the extent that specific publications are discussed above in this Description of the Related Art Section, these discussions should not be taken as an admission that the discussed publications (for example, published patents) are prior art for patent law purposes. For example, some or all of the discussed publications may not be sufficiently early in time, may not reflect subject matter developed early enough in time and/or may not be sufficiently enabling so as to amount to prior art for patent law purposes. To the extent that specific publications are discussed above in this Description of the Related Art Section, they are all hereby incorporated by reference into this document in their respective entirety(ies).